J. B. THOMPSON, JR., J. WILLARD GIBBS, AND THE EDUCATION OF PETROLOGISTS

J. B. Thompson, Jr. (1921 - 2011) taught phase equilibria to petrology students based on the masterwork of J. Willard Gibbs (1839 – 1903), “On the Equilibrium of Heterogeneous Substances” (Longmans Green, New York, 1906). In his accepting the challenge of interpreting Gibbs’ difficult 19^th century text for 20^thcentury students, one has proof of Jim’s dedication to the highest ideals of scholarship and teaching.

Jim’s penciled marginal note in his copy of Gibbs rightly identifies eq. 12 as the “starting point of chemical thermodynamics”. Jim followed Gibbs’ derivation of eq. 98 from the integrated form of eq. 12 in deriving the phase rule and in formulating analytical expressions of the equilibria of mineral assemblages containing any number of phases and components.

Jim taught Gibbs’ graphical analysis of phase equilibria so that petrologists could recognize equilibrium mineral assemblages at a glance. His exposition of Gibbs’ thermodynamics opened a new world of rigorous deductions on the conditions of origin of those beautiful turkey-track andalusites, kyanite-staurolite schists, and radiating sheaves of giant amphibole crystals.

Jim’s mineralogy used transparently clear models: teaching single- and double-I-beam chains led to discoveries of triple-I-beam silicates (Jimthompsonite and Clino-jimthompsonite). His field mapping was inspirational: He projected three-dimensional structures of alpine tectonics onto two-dimensional outcrops of the forests of New England and made sense of those damned mossy ledges buried in pucker brush.

Jim opened the eyes of many to the internal beauties of reactions hidden inside crystals. Adularia-orthoclase-sanidine: same chemistry but different site distributions as increasing temperature disorders Al-Si distributions. Reminds this writer of the latest hot thing in stable isotope geochemistry: clumped isotopes. My, how Jim would have loved that!

I honor the memory of Jim Thompson whose impact was so profound on so many. His heritage lives on in the work of his students and of their students. Thank You Jim!